General aviation in the United States is often considered an industry in decline. The number of active pilots has shown a steady decrease for several decades. In the year 1980, for example, there were about 360,000 active private pilots, while, in 2009, there were only about 220,000 active pilots remaining. This rapid decline has been attributed to many causes. One likely cause is the ever-increasing expense of flying and flight training Much of this expense can be attributed to the high costs of aviation gasoline. Most general aviation piston aircraft require 100-octane gasoline. Presently, 100-octane aviation gasoline sells for several dollars more than the gasoline used in automobiles. A common piston aircraft for flight training, the Cessna 172, typically burns over nine gallons of gasoline per hour.
At the same time, general aviation has been targeted as an unwanted source of pollution. Aviation gasoline with 100 octane contains significant amounts of lead. In fact, aviation gasoline is one of the few fuels in the United States that still contain lead, leaving it as the single largest source of lead emissions in the country. There is, as a result, ongoing efforts to legislate leaded aviation gasoline out of existence. Alternative, unleaded gasolines that can be used as a drop-in replacement for leaded aviation gasoline are under development, but are very slow to gain governmental approval and any kind of significant distribution.